Subject: 24.4; Eshell histfile symlinks not followed
From: Philip Hudson <[email-masked]>
To: [email-masked]
Date: Wed, 21 Nov 2018 23:09:16 +0000
List-Id: <debbugs-submit.debbugs.gnu.org>

If the file named by the value of option `eshell-history-file-name' is
a symbolic link, then it will be replaced and overwritten instead. It
should be dereferenced (followed) first, and its target file should be
replaced and overwritten.

The attached patch uses function `file-truename' to fix this. The
patch was made using source cloned from git savannah HEAD today, which
I think is version 26.1.90, based on ChangeLog.3 in the cloned repo.

In GNU Emacs 24.4.1 (x86_64-pc-linux-gnu, GTK+ Version 3.14.5)
of 2017-09-12 on hullmann, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11604000
System Description: LMDE 2 Betsy

-- 
Phil Hudson                  http://hudson-it.ddns.net
Pretty Good Privacy (PGP) ID: 0x4E482F85
diff --git a/lisp/eshell/em-hist.el b/lisp/eshell/em-hist.el
index 62e2f57..f866dfd 100644
--- a/lisp/eshell/em-hist.el
+++ b/lisp/eshell/em-hist.el
@@ -466,15 +466,16 @@ lost if `eshell-history-ring' is not empty.  If
 Useful within process sentinels.
 
 See also `eshell-read-history'."
-  (let ((file (or filename eshell-history-file-name)))
+  (let* ((file (or filename eshell-history-file-name))
+	 (resolved-file (file-truename file)))
     (cond
      ((or (null file)
 	  (equal file "")
 	  (null eshell-history-ring)
 	  (ring-empty-p eshell-history-ring))
       nil)
-     ((not (file-writable-p file))
-      (message "Cannot write history file %s" file))
+     ((not (file-writable-p resolved-file))
+      (message "Cannot write history file %s" resolved-file))
      (t
       (let* ((ring eshell-history-ring)
 	     (index (ring-length ring)))
@@ -489,7 +490,7 @@ See also `eshell-read-history'."
               (insert (substring-no-properties (ring-ref ring index)) ?\n)
 	      (subst-char-in-region start (1- (point)) ?\n ?\177)))
 	  (eshell-with-private-file-modes
-	   (write-region (point-min) (point-max) file append
+	   (write-region (point-min) (point-max) resolved-file append
 			 'no-message))))))))
 
 (defun eshell-list-history ()